It is primarily Hinduism that believes and promotes the concept of Hindu Trinity consisting of Lord Brahma, Lord Vishnu and Lord Shiva. Hindus believed in existence of God Almighty and also the world of souls’ atmans. This is contrary to the western belief. Not many people world over outside the Hindu fold believed in existence of world of souls atmans.
And moreover belief in self that we are primarily a spirit, soul atman manifesting human form!
The analogy of evolution of life is best detailed in Hinduism in form of various human manifestations taken by Lord Vishnu. Every religion has its own story to tell. It is primarily Hinduism that explained the concept of God Almighty, Brahman in Hinduism via three attributes namely Brahma, Vishnu and Mahesh.
For understanding Hinduism in entirety, precepts of spirituality detailed in Bhagavad Gita have to be assimilated by the western world. Even though the Hindu Trinity of Brahma, Vishnu and Shiva do not form part of spirituality, it explains well the fundamentals of evolution. Distinguishing right from wrong, truth from false at every stage of spiritual pursuit we can understand more about different manifestations of Lord Vishnu.
Allegorically, spiritually Lord Vishnu represents a liberated soul atman, a pure soul atman. A liberated soul atman is one who in absence of dross impurities within need not manifest a human body again. The need to manifest a new body by this pure soul atman ceases to exist.
Lord Vishnu is always shown lying on a bed of Adi Shesha in Mahasagar (Great Ocean) with Lakshmi by the side. Adi Shesha represents the awakened kundalini. Mahasagar represents the entire cosmos. Indulging in spirituality detailed in Bhagavad Gita, human beings initially reached state of enlightenment, self realization god realization. The moment this self realized soul left mortal frame one became a pure soul atman, a liberated soul atman in the cosmic journey of life!
Compared to Lord Vishnu Lord Shiva represents an enlightened one, a self realized soul… one stage before reaching state of liberation from cycle of birth and death.